Powder metallurgical method

ABSTRACT

A powder metallurgical method includes preparing a liquid lubricant by mixing ethylene bis stearamide 60 to 70 wt % and erucamide 30 to 40 wt % at 150 to 170° C. in a high temperature stirring process. A pulverized solid lubricant is prepared by cooling the liquid lubricant to form a solid and pulverizing the solid. A powder metallurgy composition is prepared by mixing the pulverized solid lubricant 0.4 to 0.75 part by weight to metal-based powder  100  parts by weight, and a molded body is prepared by compression molding of the powder metallurgy composition.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of priority to Korean Patent Application No. 10-2014-0167677 filed on Nov. 27, 2014, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a powder metallurgical method. More particularly, it relates to a powder metallurgical method, capable of reducing the amount of lubricant added to a metal-based powder to a minimum amount while maintaining molding energy and ejection energy equivalent or improved level.

BACKGROUND

As engines get high power, parts for a vehicle engine and transmission should secure higher mechanical properties. As methods for increasing these mechanical properties, many molding techniques were developed, but these molding techniques are often restrictively applied due to increase of the production cost of the parts and damages to a mold when molded at high pressure and the like. Of many high density molding techniques, as a way of securing high density at a pressure similar to that of the existing general molding (400 to 700 MPa), there is a method for reducing the addition amount of a lubricant.

In a powder metallurgy field, a lubricant is used with the purpose of reducing internal friction between metal-based powder particles, evenly compressing powder metallurgy, and minimizing damage to a die on a compression molding process. However, when compression molding the metal-based powder containing the lubricant, the lubricant remains between the metal-based powder particles, thereby can't obtain a high density molded body. However, when lowering the amount of the lubricant added to the metal-based powder, there is a problem of mold damage such as mold abrasion because friction resistance between pressed powder and a mold wall is increased, and releasing force is increased when the pressed powder is released from a mold. Further, there is a limit to improve density of the pressed powder because lubricity between the powder particles is reduced during metal-based powder particle rearrangement which is accompanied by a compression molding.

On the other hand, as a method for mixing the lubricant with the metal-based powder, there are 1) a mechanical mixing method for simply mixing the lubricant and 2) a polymerization method for polymerizing monomers as a basic ingredient of the lubricant.

The mechanical mixing method comprises crushing the basic ingredients of the lubricant to the size of 25 μm or less, and then inserting the metal-based powder and the basic ingredients of the lubricant in a mixer followed by mixing thereof, and therefore there is an advantage that the process is relatively simple. On the other hand, there are disadvantages that the addition amount of the lubricant can't be reduced due to high ejection energy, and it is unfavorable to secure surface roughness of the molded body low.

The polymerization method comprises inserting a polymerization solvent into a polymerizer, inserting a monomer and a metal-based powder for manufacturing a lubricant thereinto and then heating thereof at 100° C. for polymerization. The polymerization method induces chemical bonding between molecules of the basic ingredients of the lubricant. Thus, it has an advantage of securing uniformity and low ejection energy, but has a disadvantage that the production cost is increased too much due to its complex process.

Now, in the powder metallurgy field, development of a metallurgy method, which can obtain a high density molded body as well as can maintain ejection energy low during ejection after completing compression molding, by minimizing the addition amount of the lubricant, is urgently needed.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

The present disclosure has been made in an effort to solve the above-described problems associated with prior art.

An object of the present inventive concept is to provide an improved powder metallurgical method, which manufactures a high density molded body by reducing the amount of the lubricant added to the metal-based powder to the minimum while maintaining ejection force and molding pressure at an equivalent or improved level.

To achieve the above object, in one aspect, the present disclosure provides a powder metallurgical method, which includes: preparing a liquid lubricant by mixing ethylene bis stearamide 60 to 70 wt % and erucamide 30 to 40 wt % at 150 to 170° C. in a high temperature stirring process; preparing a pulverized solid lubricant by cooling the liquid lubricant to form a solid and pulverizing the solid; preparing a powder metallurgy composition by mixing the pulverized solid lubricant 0.4 to 0.75 part by weight to metal-based powder 100 parts by weight; and preparing a molded body by compression molding of the powder metallurgy composition.

In certain embodiments, the metal-based powder may be iron-based powder.

In certain embodiments, the compression molding may be conducted under a pressure of 500 to 600 MPa.

In certain embodiments, the molded body may be ejected from a mold by adding an ejection force of 900 to 1400 Kgf.

In certain embodiments, the step of preparing a molded body further includes adding ejection force of 900 to 1100 Kgf, the molded body has a density of 7.2 to 7.3 g/cm³, and the compression molding is conducted under a pressure of 500 to 600 MPa.

Other aspects and preferred embodiments of the invention are discussed infra.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

FIG. 1 is a graph comparing ejection force depending on change of content ratio of ethylene bis stearamide and erucamide as lubricant ingredients, in manufacturing a powder metallurgy molded body by using metal-based powder 100 parts by weight and a lubricant 0.75 parts by weight, which is prepared by a high temperature stirring process;

FIG. 2 is a graph comparing ejection force, in manufacturing a powder metallurgy molded body by using metal-based powder 100 parts by weight and a lubricant 0.75 parts by weight where composition ratio of ethylene bis stearamide and erucamide is 70:30 wt %, which is prepared by a high temperature stirring process;

FIG. 3 is a graph comparing ejection force depending on change of the addition amount of the lubricant and molding pressure, in manufacturing a powder metallurgy molded body by using metal-based powder 100 parts by weight and a lubricant 0.4 parts by weight where composition ratio of ethylene bis stearamide and erucamide is 70:30 wt %, which is prepared by a high temperature stirring process;

FIG. 4 is a graph comparing ejection force depending on change of content ratio of ethylene bis stearamide and erucamide as lubricant ingredients, in manufacturing a powder metallurgy molded body according to a conventional method by using metal-based powder 100 parts by weight and a lubricant 0.75 parts by weight, which is prepared by a mechanical mixing process at room temperature;

FIG. 5 is a graph comparing ejection force depending on change of content ratio of ethylene bis stearamide and erucamide as lubricant ingredients, in manufacturing a powder metallurgy molded body according to a conventional method by using metal-based powder 100 parts by weight and a lubricant 0.75 parts by weight, which is prepared by a polymerization process; and

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodiments of the present inventive concept, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

The present disclosure relates to a powder metallurgical method, which includes: preparing a liquid lubricant by mixing ethylene bis stearamide 60 to 70 wt % and erucamide 30 to 40 wt % at 150 to 170° C. in a high temperature stirring process; preparing a pulverized solid lubricant by cooling the liquid lubricant to form a solid and pulverizing the solid; preparing a powder metallurgy composition by mixing the pulverized solid lubricant 0.4 to 0.75 part by weight to metal-based powder 100 parts by weight; and preparing a molded body by compression molding of the powder metallurgy composition. The powder metallurgical method according to certain embodiments of the present invention will be described in detail step by step as follows.

The first step is preparing a lubricant.

In certain embodiments of the present invention, an amide-based lubricant containing ethylene bis stearamide and erucamide is used as the lubricant, and undergoes a high temperature stirring process to evenly disperse the lubricant ingredients together.

Namely, in certain embodiments of the present invention, among amide-based lubricants used in the powder metallurgy field, ethylene bis stearamide and erucamide are selected, and an optimum content ratio between the two ingredients is suggested. Thus, the addition amount of the lubricant can be minimized and compression molding energy and ejection energy of a molded body can be maintained low at the same time. According to certain embodiments of the present invention, the lubricant may have composition ratio of ethylene bis stearamide 60 to 70 wt % and erucamide 30 to 40 wt %, and, in certain embodiments, have composition ratio of ethylene bis stearamide 70 wt % and erucamide 30 wt %.

Further, in certain embodiments of the present invention, an evenly dispersed liquid lubricant is prepared by stirring the lubricant having the specific composition ratio at high temperature, the liquid lubricant is cooled to be converted into a cake-type solid phase and pulverized, and then the obtained pulverized solid lubricant is mixed to metal-based powder for use.

As the conventional method for manufacturing a lubricant, often, a ‘mechanical mixing’ method is conducted at a room temperature, and therefore, there is a limit to induce an even dispersion between the lubricant ingredients. However, in embodiments of the present invention, an even dispersion between the lubricant ingredients is induced through a ‘high temperature stirring’ process wherein the lubricant ingredients are mixed while maintaining temperature inside of a mixing machine at 150 to 170° C., thereby ultimately lowers ejection energy of the molded body. Thus, it is possible to safely release a mold without abrasion of the molded body by adding only a small amount of the lubricant. If temperature of the high temperature stirring is less than 150° C. in the manufacturing process of a lubricant according to certain embodiments of the present invention, there is a limit to lower ejection energy because an even dispersion of the ethylene bis stearamide and the erucamide is not achieved as well as a molded body having high surface roughness(Ra) may be manufactured. On the other hand, if temperature of the high temperature stirring is over 170° C., the erucamide having low melting point may be oxidized, discolored and increased in viscosity, thereby crushing may be unfavorable.

Further, in certain embodiments, in order to convert the liquid lubricant prepared by the high temperature stirring process into solid phase, cooling and pulverizing is conducted by general methods. In certain embodiments, the liquid lubricant is cooled to be converted into a cake form. At this time, in certain embodiments, cooling may be conducted to the temperature around room temperature, and in certain embodiments, cooling is conducted to temperature of 10 to 30° C. The cake-type lubricant is pulverized for even mixing with the metal-based powder, and in certain embodiments, an average particle size of the pulverized solid lubricant may be maintained in a range of 10 to 40 μm.

The next step is preparing a powder metallurgy composition.

In certain embodiments of the present invention, the powder metallurgy composition is prepared by mixing the lubricant 0.4 to 0.75 parts by weight to the metal-based powder 100 parts by weight. In certain embodiments, in the step of preparing the powder metallurgy composition of the present invention, the addition amount of the lubricant may be reduced to the minimum.

The next step is preparing a high density molded body by compression molding.

In certain embodiments of the present invention, compression molding is conducted by a general metallurgy technique. In certain embodiments, the powder metallurgy composition may be filled into a die and compressed at pressure of 500 to 600 Mpa to prepare the molded body. In certain embodiments, the prepared molded body may be separated from the die by adding ejection force of 900 to 1400 Kgf.

In certain embodiments, the molded body manufactured by the above method m m ay maintain a high density of 7.1 to 7.3 g/c³. Further, according to the powder metallurgical method of certain embodiments of the present invention, compared to addition of the lubricant 0.75 parts by weight based on the metal-based powder 100 parts by weight, when the lubricant 0.4 parts by weight is added, the following extraordinary effect may be obtained. Ejection force may be reduced as much as 200 Kgf, and molding density may increase as much as 0.18 g/cm³.

The powder metallurgical method of another embodiment of the present invention may include:

i) preparing a liquid lubricant by high temperature stirring process, wherein ethylene bis stearamide 60 to 70 wt % and erucamide 30 to 40 wt % are mixed at 150 to 170° C.;

ii) preparing a pulverized solid lubricant by cooling the liquid lubricant to form a solid and pulverizing the solid; iii) preparing a powder metallurgy composition by mixing the lubricant 0.4 to 0.5 parts by weight to metal-based powder 100 parts by weight; and

iv) preparing a molded body having density of 7.2 to 7.3 g/cm³ by compression molding the powder metallurgy composition under pressure of 500 to 600 MPa, and then applying ejection force of 900 to 1100 Kgf thereto are conducted.

EXAMPLES

The following examples illustrate certain embodiments of the invention and are not intended to limit the invention.

Example 1 Identification of Change in Ejection Force Depending on Composition Ratio of Ethylene Bis Stearamide and Erucamide

Each lubricant was prepared by changing composition ratio of ethylene bis stearamide and erucamide as lubricant ingredients to 50:50, 55:45, 60:40, 70:30 wt %. Namely, a liquid lubricant was obtained by stirring the lubricant ingredients at high temperature of 160° C. for 60 min. And, the liquid lubricant was cooled while stored at room temperature to obtain a cake-type lubricant, and then pulverized to obtain a solid lubricant in a range of 10 to 40 μm.

As iron-based powder, HSPP (Hyundai Steel, pure iron powder) was used. The lubricant 0.75 parts by weight prepared above was mixed to iron-based powder 100 parts by weight to prepare a powder metallurgy composition. The powder metallurgy composition was put into a die, and then molding pressure of 500 MPa was applied thereto to obtain a molded body having density of 7.12 g/cm³.

In order to identify ejection force depending on composition ratio of the ethylene bis stearamide and the erucamide constituting the lubricant, ejection force was measured based on MPIF Standard 45, and the result is shown in FIG. 1.

According to FIG. 1, it could be found that as composition ratio of the ethylene bis stearamide and the erucamide was changed to 50;50, 55:45, 60:40, 70:30 wt %, ejection force was reduced. Namely, as the content of the erucamide contained in the lubricant was decreased, ejection force was reduced from 1400 kgf to 1100 kgf, and when composition ratio of the ethylene bis stearamide and the erucamide was 70:30 wt %, ejection force was the lowest as 1100 kgf.

Example 2 Identification of Change in Density of Molded Body Depending on Addition Amount of Lubricant

According to the metallurgy method of Example 1, a molded body was manufactured by using a solid lubricant whose composition ratio of the ethylene bis stearamide and the erucamide is 70:30 wt %, and density change of the molded body was measured as changing the addition amount of the solid lubricant to 0.75 parts by weight or 0.40 parts by weight, respectively, based on the iron-based powder 100 parts by weight.

In FIG. 2, the lubricant 0.75 parts by weight based on the iron-based powder 100 parts by weight is added and ejection force is measured three separate times (labeled as first, second, and third). A comparison of the results is represented in a graph. According to FIG. 2, ejection force was low as 1100 kgf, and a molded body having density of 7.11 g/cm³ was manufactured by applying molding pressure of 500 MPa.

In FIG. 3, the lubricant 0.40 parts by weight based on the iron-based powder 100 parts by weight is added, the addition amount of the lubricant and molding pressure changes, compared with FIG. 2, and ejection force is measured three separate times (labeled as first, second, and third). A comparison of the results is represented in a graph. According to FIG. 3, ejection force was very low as 900 kgf, and a molded body having density of 7.30 g/cm³ was manufactured by applying molding pressure of 500 MPa.

According to FIG. 2 and FIG. 3, it could be found that when using the lubricant whose composition ratio of the ethylene bis stearamide and the erucamide is 70:30 wt %, it is possible to lower ejection force by 200 kgf as the amount of added lubricant is reduced from 0.75 parts by weight to 0.40 parts by weight. It is also possible to improve density of the molded body by as as much as 0.19 g/cm³.

Comparative Example 1 and Comparative Example 2 Comparison of Ejection Force in Conventional Metallurgy Method

A powder metallurgy composition was manufactured by mixing iron-based powder and a lubricant by the method of Example 1, but for preparing the lubricant, mechanical mixing method at room temperature (Comparative Example 1) or heating polymerization method (Comparative Example 2) as the conventional method was conducted.

In FIG. 4 and FIG. 5, the results of measuring ejection force as changing composition ratio of the ethylene bis stearamide and the erucamide constituting the lubricant to 50;50, 55:45, 60:40, 70:30 wt % were shown, respectively.

The results of comparing Example 1 and Comparative Examples 1 and 2 are summarized in the following Table 1.

TABLE 1 Comparative Comparative Section Example 1 Example 2 Example 1 Example 2 Lubricant Constitution Content ratio (Ethylene bis stearamide:Erucamide) (wt %) #1: 50:50, #2: 55:45, #3: 60:40, #4: 70:30 Added amount 0.75 0.4 0.75 0.75 (part by weight) Mixing method 160° C. High Room Polymerization temperature temperature mixing mixing Ejection Force (kgf) 1100~1400 900 1500~2250 1500 Molding pressure (MPa) 500 500 500 500 Molded Density (g/cm³) 7.12 7.30 7.11 7.10 body Surface 0.6 0.8 1.1 0.9 roughness (Ra)

As compared in the above, according to the metallurgy method of certain embodiments of the present invention, a high density molded body can be manufactured as reducing the added amount of a lubricant based on weight of metal-based powder as well as having density of up to 7.3 g/cm³ by lowering ejection energy, by manufacturing powder metallurgy composition by mixing ethylene bis stearamide and erucamide constituting a lubricant at high temperature while limiting the composition ratio thereof to a certain range. Further, according to the result of the above Table 1, it is also possible to maintain a low surface roughness.

Embodiments of the present invention have the effects of maintaining molding energy and ejection energy low while increasing density of a molded body and improving surface roughness by using only a small amount of the lubricant by a lubricant manufacturing process to which use of a lubricant with a certain composition and a high temperature stirring process are introduced.

Thus, according to the powder metallurgical method of certain embodiments of the present invention, a molded body having high density of 7.3 g/cm³ can be manufactured by reducing the amount of a lubricant up to 0.4 parts by weight, based on metal-based powder 100 parts by weight.

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents. 

What is claimed is:
 1. A powder metallurgical method, comprising: preparing a liquid lubricant by mixing ethylene bis stearamide 60 to 70 wt % and erucamide 30 to 40 wt % at 150 to 170° C. in a high temperature stirring process; preparing a pulverized solid lubricant by cooling the liquid lubricant to form a solid and pulverizing the solid; preparing a powder metallurgy composition by mixing the pulverized solid lubricant 0.4 to 0.75 part by weight to metal-based powder 100 parts by weight; and preparing a molded body by compression molding of the powder metallurgy composition.
 2. The powder metallurgical method of claim 1, wherein the metal-based powder is iron-based powder.
 3. The powder metallurgical method of claim 1, wherein the compression molding is conducted under a pressure of 500 to 600 MPa.
 4. The powder metallurgical method of claim 1, further comprising: ejecting the molded body from a mold by adding an ejection force of 900 to 1400 Kgf.
 5. The powder metallurgical method of claim 1, wherein the step of preparing a molded body further comprises adding an ejection force of 900 to 1100 Kgf, the compression molding is conducted under a pressure of 500 to 600 MPa, and the molded body has a density of 7.2 to 7.3 g/cm³. 